Wood pulp and process of making the same



Patented M'Q 24, 1932 4 UNITED STATES PATENT OFFICE JOHN I). RUE, O1 MADISON, WISCONSIN, SIDNEY D. WELLS, OF QUINCY, ILLINOIS, AND

M018 G. RLWLING, OI IADISON, WISCONSIN, ASSIGNOBS TO ARTHUR H. m SECRETARY OF AGRICULTURE OF THE UNITED STATES WOOD PULP AND PLOOEBB OI MAKING THE SAME Ho Drawing.

This invention relates to pulp products made from vegetable fibers such as are obtained from wood, and more particularly to a product suitable for the inanufacture of 5 corrugated paper board.

Corrugated board, or box board, such as 1s 7 at present used in the industry, consists almost exclusively of straw board, that is to say,

board manufactured from pulp made of 1 straw.' Such board has certain inherent characteristics which peculiarly fit it for its use, namely, it is flexible enough topass through the corrugating machine without breaking, and, after being corrugated, it has sufficient 5 strength and stiflness to withstand all ordinary shocks and blows to which boxes or containers are usually subjected.

The general object of the present invention is to provide a pulp made from'wood, and

an especially waste wood, and the cheaper grades of wood, from-which pulp may be manufactured a'corrugated board having all of the properties and advantages of the straw board heretofore employed.

To this end, we have discovered that if wood chips are subjected to a mild chemical digest-ion with certain kinds of solutions, under certain conditions of temperature and pressure, for a limited length of time, and the thus softened chips then treated mechanically to 0 en up and separate the fibers, a pulp is pro uced containing a substantial amount of the ori in'al lignin, and which can be made into oards having the requisite flexibility and strength or stifi'ness for corrugating.-

Our improved process is especially applicable to chestnut wood, but can also be effectively employed with other deciduous woods, such as aspen, beech, birch, cottonwood, gum, maple, willow, etc. By the term wood as used in this specification and claims we mean to include also the bark of a tree. By the term chips we mean to include any more or less finely divided pieces of the trunk, branches, twigs, or bark, from which the tannin may or may not have been previously extractedj We also contemplate the use of hardwood waste, consisting of the ref- 50 use from some industry utilizing hard woods.

Application filed Input 4, 1928. Serial- Ii'o. 197,171.

In preparing our improved pulp, we proceed as follows: We take a suitable quantity of wood chips or the like,'and place in a digester with an aqueous solution of chemical salts. It is important that these salts be of a substantially neutral character free from acids or alkalies such that when they are dissolved in water, .the resulting solution shall have a hydrogen ion concentration corresponding to between 5 and 13 in the pH scale.

In practice, we prefer to use sodium salts such as a mixture of sodium sulphite with the sodium and sodium hydrogen salts of weakly ionized polybasic acids, examples of which are sodium carbonate, sodium bicarbonate, sodium borate. One satisfactory mixture consists of sodium sulphate, sodium carbonate and sodium bicarbonate'andthese may be mixed in any desired proportion. The total amount of salts emplo ed should not be in excess of twenty poun s for each a one hundred pounds of oven dry wood material or chips.

Heat is then applied to the digester so as to cause the solution to boil, the pressure being maintained at seventy to eighty pounds per square inch above atmospheric pressure, and the temperature accordingly being between 125 and 170 C. The use of this temperature is essential to secure the desired results. The boiling is continued for a period not exceedin six hours, and at the end of this time, the chlps are dumped or blown out of the digester and are given a mechanical treatment without any intermediate washing.

The mechanical treatment consists in subjecting the softened chips to a pounding and rubbing action in such a way as to open up and separate the fibers longitudinally without grindin or cutting them transversely,'so that the rs retain substantially their original length. Such a mechanical treatment, for example can be produced by subjecting the chips to the action of a rod mill,

'kollergang or swing hammer shredder.

As a result of this mechanical treatment, the material is reduced to a pulp suitable for the making of corrugating boards, as above described.

The acid or alkaline solutions heretofore used in the chemical pulping of wood have had the efiect of dissolving some of the cellulose. In our improved process, however, in which only neutral salts are used and in which the time and temperature are suitably limited, little or none of the cellulose is attacked and only a portion of the lignin is ehminated. A substantial amount of this lignin or cementing material is allowed to remain in the pulp, and this has the result of giving to the pa r board manufactured therefrom the sti ness and rigidit necessary to cause the corrugations to hol their shape.

In practice, we find that the chemlcal treatment within the limits of temperatures, pressures, and strength of solutions above described results in the production of a pulp consisting of from seventy to ninety percent cellulose and thirty to ten percent of lignin.

By the term lignin is meant that residue which is obtained by the Ost and Wilkening method of estimating lignin in lignocelluloses, and by cellulose is meant the residue obtained by the application of the Cross and Bevan method of estimating cellulose in lignocelluloses. The Ost and Wilkening and Cross and Bevan methods alluded to above may be applied to our product for purposes of analysis, or to the wood, and are well known methods of analysis.

By the term pulp product as described and claimed herein is meant a roduct made directly from wood chips and t us composed of one type of material as contrasted to a compound m xed from two or more kinds of pulp of which news print paper is an examle. p This application is a continuation in part of our application Serial 100,685, filed April 8, 1926, treatment of wood for production of p What we claim is 1. The process of making wood pulp product, suitable for the manufacture of corrugated board, the said process comprising subjecting wood chips to a mild chemical digestion with a substantially neutral solution containing sodium sulphite and the sodium salt of a weakly ionized polybasic acid, and continuing the digestion until the wood chips are softened to a uniform degree throughout but not ulped into their ultimate fibers and then mechanically treating the softened chips to open up and separate the fibers.

2. The process of making a wood pulp product, suitable for the manufacture of corrugated board, the said process comprising subjecting wood chips to a mild chemical digestion with a substantially neutral solution containing a substantial mixture of two or more sodium salts and one of which is the sodium salt of a weakly ionized polybasic acid, and continuing the digestion until the wood chips are softened to a uniform degree throughout but not pulped into their ultimate fibers and then mechanically treating the chi s to open up and separate the fibers.

3. T e process of making a wood pulp product, suitable for the manufacture of corrugated board, the said process comprisin subjecting wood chips to a mild chemica digestion with a substantially neutral solution consistin of a mixture of sodium sulphite and sod um carbonate, and continuin the digestion until the wood chips are so tened to a uniform degree throughout but not pul ed into their ultimate fibers and then mec anically treating the softened chips to open u an separate the fibers.

4. T e process of making a wood pulp product, suitable for the manufacture of corrugated board, the said process comprising subjectin wood chips to a mild chemical digestion with a substantially neutral solution containing a mixture of sodium sulphite, sodium carbonate, and sodium bicarbonate, and then mechanically treating the softened chips to open up and separate the fibers.

5. The process of making a wood pulp product, suitable for the manufacture of 'corru ated board, the said process comprising su jecting wood chips to a mild chemical digestion for not exceeding six hours, at a temperature between 125 C. and 170 C. and continuing the digestion until the wood chips are softened to a uniform degree throughout but not pulped into their ultimate fibers with a substantially neutral solu-' tion containin sodium salts at least one of which is a so ium salt of a weakly ionized polybasic acid, and then mechanically treatmg the softened chips to open up and separate the fibers.

6. The process of making a wood pulp product, suitable for the manufacture of corru ated board, the said process comprisin su jecting wood chips to a mild chemical d1- gestion for not exceedin six hours, at a temperature between 125 a substantially neutral solution containing sodium salts at least one of which is a sodium salt of a weakly ionized polybasic acid in amount not more than twenty ounds for each hundred pounds of oven ried chips, and continuin the digestion until the wood chips are so ened to a uniform degree throughout but not pulped into their ultimate fibers and then mechanically treating the softened chips to open up and separate the fibers.

7. The process of making a wood pulp product, suitable for the manufacture of corrugated board, the said process comprising bolling wood chips in a substantially neutral solution containing a plurality of salts at least one of which is the sodium salt of a weakly ionized polybasic acid less than twenty and more than four parts by weight of chemicals for each hundred parts of oven dry chips, at a pressure not exceeding eightyand 170 0., with pounds, above atmospheric, and for a period not exceeding six hours, and continuing the digestion until the wood chips are softened to a uniform degree throughout but not pulped into their ultimate fibers and then mechanically treating the softened chips to open up and separate the fibers.

8. The process of making a wood pulp product, suitable for the manufacture of corrugated board, the said process comprising subjecting wood chips to a mild chemicaldigestion with a substantially neutral solution consisting of a mixture of sodium sulphite with the sodium salt of a weakly ionized polybasic acid, and continuing the digestion until the wood chips are softened to a uniform degree throughout but not pulped into their ultimate fibers and then mechanically treating the softened chips to open up and separate the fibers.

9. The process of making a wood pulp product, suitable for the manufacture of corrugated board, which process comprises subjecting wood chips to a mild chemical digestion with a substantially neutral solution containing a mixture of an alkali metal sulphite, an alkali metal carbonate and an alkli metal bi-carbonate, and then mechanically treating the softened chips to open up and a separate the fibers.

10. The process ofmaking a wood pulp product, suitable for the manufacture of corrugated board, which process comprises subjecting wood chips to a mild chemical digestion with a substantially neutral solution containing a mixture of a sul hite, a carbonate and a bi-carbonate, and t en mechanically treating the softened chips to open up and separate the fibers.

In testimony whereof, we our signatures.

JOHN D. RUE. SIDNEY D. WELLS. FRANCIS G. RAWLING. 

